1. Field of the Invention
The present invention relates to a new image forming method for obtaining color images on separate materials by using light-sensitive elements for photographing by a heat developing process. More particularly, in this new image forming method for obtaining color images on simple heat developing process, an image forming method in which a light-sensitive element exhibits an excellent preservablity after heat-development.
2. Description of the Related Art
In a method regarded as conventional color photography, what is known as a color negative contains a layer in which a yellow dye image is formed by recording blue light, a layer in which a magenta dye image is formed by recording green light, and a layer in which a cyan dye image is formed by recording red light. During the development step, a dye image is formed by the reaction (known as "coupling") of a coupler and an oxidized product which has been formed by oxidizing a developing agent in a process of reducing silver halide grains containing a latent image to silver. Both the undeveloped silver halide and the developed silver are removed in the subsequent bleaching and fixing processes. Color paper is then exposed through the negative dye image thus obtained and a color print is acquired through developing, bleaching, and fixing processes similar to the above processes.
Further, a method for forming a color image is also known in which image information contained in the above-described color negative is photoelectrically read, then image processing is performed to give image information for recording, and a color image is formed on other print material by using this image information. In particular, digital photo printers have been developed in which a light-sensitive element such as a color paper is exposed by scanning with recording light modulated by digital signals modulated in accordance with the above-described image information to obtain a finished print. An example of this technique is described in Japanese Patent Application Laid-Open (JP-A) No. 7-15593.
The above-described method requires normal wet developing, bleaching and fixing, and the process is complicated. Moreover, the developing solution used for wet developing is a strong base, therefore it is a dangerous chemical. Further, this developing solution degrades markedly, and control to keep the activity of the developing solution constant is complicated. This control method has been recently improved, however, it is still insufficient.
On the other hand, a simple and rapid method utilizing heat developing has been developed as a processing method for light-sensitive elements using silver halide. "Pictorography" and "Pictorostat" manufactured by Fuji Photo FilmCo., Ltd. are well known examples thereof. However, these are color print materials, and a color light-sensitive element for photographing using heat developing method has not yet been known.
As a heat developing method, there has been known a method in which heat developing is conducted in the presence of a small amount of water and a base and/or base precursor. An example of this method is described in Japanese Patent Application Publication (JP-B) No. 2-51494. However, in the image forming method as described therein, a dye donating material is used which manifests reducing properties for light-sensitive silver halide and reacts with the light-sensitive silver halide when heated to release a hydrophilic dye, and the dye released in heat development is transferred on an image receiving material which is used as a color print.
It has been found that when a light-sensitive element containing a color developing agent (hereinafter, sometimes referred to as simply "developing agent") which is highly stable in the absence of a base and a coupler is used in combination with a processing element containing a base and/or base precursor, and heat developing is conducted in the presence of a small amount of water, to form an image based on non-diffusive dye on the light-sensitive element, an image having excellent granularity and sharpness is obtained, and when the image information thus obtained is outputted onto another recording material such as color paper, heat developing color print material and the like, an excellent color image can be obtained. In this case, it is possible to conduct rapid processing with satisfying high preserving stability required for material for photographing, since the light-sensitive element and the base are separated before development. Further, the method in which a colorless color developing agent and a coupler are used is advantageous from the point of sensitivity which is extremely important for materials for photographing, in comparison with the method in which a dye releasing type compound is used.
However, in such a structure, problems of insufficient storability such as occurrence of unintended fogging and staining after heat development arise when a light-sensitive element is allowed to stand after heat development.